Anti-back draft damper



Nov. 19, 1963 D. R. RUEGSEGGER 3,

ANTI-BACK DRAFT DAMPER Filed Dec. 4, 1961 2 Sheets-Sheet 2 United States Patent 3,111,381 ANTl-BACK DRAFT DAMPER Donald R. Ruegseggcr, Detroit, Mich, assignor to Margaret M. Melons, Grosse Pointe, Mich. Filed Bee. 4, 1961, der. No. 156,567 2 Claims. (ill. l-356) This invention relates to anti-back draft dampers and particularly to improvements thereon which improve their operation, render their installation easier, reduce their cost of manufacture, and greatly simplify their packaging and shipment.

Modern buildings such as oliice buildings, food warehouses, research institutions, hospitals and homes are often provided with ventilation ducts which allow fresh air to enter the rooms either by natural or forced draft. Gutlet ducts are also provided, usually in the ceiling of the rooms, and may connect into a main outlet duct extending through the building roof, or each may extend directly to and through the roof for allowing the heated air in the rooms to naturally pass upwardly and out of the building or to be forced therefrom by means of the pressure of forced fresh air entering the building.

In most buildings it is very desirable to maintain the rooms under higher than atmospheric pressure so that dust laden air will not have a tendency to enter the building through cracks and other small openings therein. In these buildings, the fresh air which is allowed to enter therein must pass through filtering devices so that the dust content of the air may be controlled.

in order to maintain suificient pressure in the building to prevent this seepage of dust laden air While controlling the pressure in the building to prevent discomfort of the occupants thereof, anti-back draft dampers are commonly employed in the outlet ducts which as aforesaid extend through the roof of the building. These dampers are conventionally provided with a frame which pivotally supports a damper blade and which is adapted to fit fairly snugly into the outlet ducts. The damper blades are mounted in the frame off center so that they wi l close when the pressure in the building does not exceed a certain minimum and will open when this minimum pressure is attained. In addition to maintaining a desired pressure within the building, the dampers, by closing, prevent a flow of dust laden air through the outlet ducts into the building when the pressure therein becomes less than outside air pressure. This situation may occur, for example, when wind gusts cause sudden pressure increases in the outlet ducts tending to force air backwardly therethrough.

In order that these dampers may have versatility in their application to various types of buildings and in their operation Within these buildings, the blades of these dampers are conventionally provided with adjustable weight means for varying the resistance of these blades to opening. For example, where a relatively high pressure is desired in a building such as in food storage warehouses and the like where it is very desirable to more positively prevent the in seepage of dust laden air, the blades are more heavily loaded in their closed positions than they are, for example, in a home.

Dilliculty has been encountered, however, in providing these damper blades with adjustable weight means which can function properly to provide the desired closing force to the blade under certain conditions which frequently arise in the use of these dampers. One of these conditions is that the damper frame is not horizontally disposed in the duct but is tilted therein so that the blade in opening to its wide open position may have to travel beyond its perpendicular position relative to the frame, and in closing may have to travel beyond its horizontal ice position relative to the duct. Another of these conditions is that the damper frame is tilted in the opposite direction in the duct so that when the blade is perpen dicular to the frame, the blade is overcentered with respect to the vertical axis of the duct.

The tilted positions of the damper frame within the duct may result from improper positioning of the angle iron supports or screws for the frame, or from inaccuracies in the dimensions of the duct. For example, if the duct is too narrow in one direction, the damper frame may have to he fitted therein at an angle.

These structural conditions as will become evident from further discussion, present problems due to the fact that it is desirable to so construct the damper that the blade may open wide and present a minimum of ob struction to the outgoing air particularly Where forced draft means is provided and it is not desirable to have an excessively high static pressure existing in the room, and further, that it is desirable to provide a closing weight which may be adjusted to provide slight resistance to opening of the blade.

in the past, projecting weight means have been provided on the damper blade, and projecting stop means have been provided on the frame for engaging the blade and preventing overtravel thereof in certain directions. Aside from the fact that these prior constructions have not satisfactorily performed in all operating situations contemplated by applicant, these weight and stop means which have extended outwardly from the plane of the damper provide a bulky damper.

As one might anticipate, the economics of such bulky dampers are somewhat aske-w, due to excessive packaging, handling and shipping costs. 'In this regard it is noted that several dampers cannot conveniently be stacked for shipment. Should the manufacturer, on the other hand, leave certain parts of the damper disassembled for shipment, the cost of assembly at the building site would be increased. In regard, it is particularly noted that manufacturers of these dampers are disposed to make as much use as they can of manufacturing techniques such as riveting and the like which allows economical manufacture at the manufacturing plant but does not allow shipment of separate parts and assembly thereof at the place of installation.

The main objects, therefore, of the invention are: to provide an anti-back draft damper which is versatile in its uses and adaptation to various size ducts and which has rugged but sensitively adjustable weight means for providing closing force to the damper blade regardless of its position relative to the frame; and to provide an economical compact damper of simple construction which is easy to manufacture, package and ship.

Further objects, advantages and novel features of the invention will become apparent from the following description taken in conjunction with the appended claims and drawings wherein:

FIGURE 1 is a side view of the damper mounted in a metal duct with the front wall of the duct removed;

FIGURE 2 is a sectional view taken along the line 2--2 of FEGURE l;

FlGURE 3 is a sectional view taken along the line 3-3 of FEGURE 1 showing one of the blade pivots;

FlGURE 4 is a sectional view taken along the line 44 PlGURE 1;

FIGURE 5 is a sectional view taken along the line 55 of FIGURE 2; and

FIGURE 6 is a perspective view of the damper.

In the drawing:

A duct 1%, usually of sheet metal, of rectangular or square cross section receives the frame 12 of a damper 14. The frame 12 is shown horizontally disposed in the duct and secured therein by sheet metal screws 15. Other 3 means may be provided for supporting the damper frame such as angle :iron sections secured to the inside of the duct and engaging the underside of the frame. Regardless of Le means employing to support the damper, it often occurs that the damper is not positioned horizontally in the duct but is disposed at an angle therein as represented by the dotted lines A and B in FIGURE 1. This may be caused by improper placement of the screws or angle iron supports in the duct, or by the duct being too small for one dimension of the damper frame which necessitates its angular positioning therein.

The blade 16 is shown in FIGURE 1 in its wide open position representing maximum air flow through the duct. Stop means for limiting the swinging motion of the blade toward its full open position is not provided for reasons set forth below. When the frame is in the horizontal position as shown in FIGURE 1, or is in the angular position as shown by the dotted lines A in FIGURE 1, the blade upon opening may have a tendency to overtravel to the position shown by its dotted lines A. As will become evident from the following description the improved weight means itself, Without the need for any projecting stops on either the frame or blade, will tend to prevent this overtravel and urge the blade from its over-travel position to its full open position shown by the solid lines. This will allow the blade to be properly moved toward its closed position by a sudden downdraft in the duct it and also upon a slower decrease in the pressure differential across the blade. It is noted that if the blade overtravelled on opening and the proper closing weight means were not provided, a sudden let down in pressure in the room or a sudden wind gust elevating the pressure in the duct above the damper would tend to hold the blade open and allow dust laden air to flow into the room. it is for this reason that some of the prior dampers employ stops to prevent this overtravel of the blade. in this regard it the frame 12 were in the position represented by the dotted lines B in FIGURE 1, the blade 16 would not be able to open fully if stops were provided for preventing overtravel of the blade past its vertical position relative to a horizontally disposed frame.

When the frame is positioned in the duct as shown by dotted lines B in FIGURE 1, the blade 16 must actually travel past the horizontal upon closing. The provision of a closing weight on the blade tending to close the same would seem to be the simple answer to this problem; however, its location and configuration becomes critical when it is considered that the closing force must be readily adjustable and must tend to close the blade when the blade is in either of the positions represented by dotted lines A, a vertical wide open position, or an angular position represented by dotted lines B. The description below the dam-per will readily show how this is accomplished.

The frame comprises a pair of end-sections l8 and 2t) and a pair of side sections 22. and 24. Section 18 is formed in the shape of a channel having an outside flange 26, an inside flange 28 and a connecting web 30. The ends of flange 28 are cut back to positions 32 and 34 for a purpose hereinafter explained. Section has a right angle shape and comprises flanges 36 and 38. Sections 22 and 24 are channel shaped and identically formed with outer flanges 40, inner flanges i2 and connecting webs 44-. The cut back flange 28 of section 18 allows the webs 4dof sections 22 and 24 to rest on the web 3% of section 18 and be welded thereto as at 4-6. The webs 44 are similarly welded to the flange 3% of section 29 to thereby provide a welded rectangular baflie frame.

The blade 16 comprises a single sheet metal piece formed to provide a main portion 4-8, a counterbalancing portion and a web portion 52 formed at right angles to portions 43 and 5t). Stidening flanges 54- and as are provided respectively on portions 4-8 and 5b. The means for pivotally mounting the blade on the frame comprises a metal strip 58 secured to web portions 52 by suitable means such as rivets S9 or spot welds and having end portions so and 62 bent at right angles to the web portion 52 and respectively disposed in notches 64 and es formed in the end portions of web 52. and the adjacent edges of portion 48 of the lade. As shown in FIGURE 3 which represents the pivotal mounting of one side of the blade, the upturned end so of member 5'8 is pivotally secured to the inner ge d2 of channel section 22 by means of a rivet 63 loosely headed to allow free pivotal motion between the blade and frame. The opposite side of the blade is mounted in identical manner to the inner flange -2 of member 24.

Fortions and 5-3 of the blade are made suficiently wide so that the edge portions will overlap the tops of the adjacent inner flanges 42 of members 22 and 24 when the blade is rotated clockwise relative to FEGURE 1 to its closed position. This overlapping assists in obtaz'ming a dust seal between the blade and the frame. A sound deadening strip of fabric material such as felt is adhesively secured to the inside of flange 28 of section 18 and projects sli htly above the top thereof to engage the underside of portion 43 of the blade when the blade is closed. Strip 79 thereby prevents portion 48 from striking against the top of flanges 42. of sections 22 and 24 as well as flange 28 of section 18. Though the strip 76 as shown in FIGURE 5 does not allow portion 4-8 of the blade to completely close, the strip allows it to close sufficiently to provide an adequate dust seal particularly since strip 7% provides an excellent dust seal for a portion of the blade. A strip 72 of felt or other suitable sound deador sealing material is adhesively secured to the top side 7d of flan es 33 of angle section 2% and extends on top 74 between the flanges 42 of channel sections 2.2 and 24. End portions 76 and 78 of strip 72 which lie beyond the edge 8b of flange $8 are extended downwardly and under the bottoms of the webs 44 of sections 22 and 24 and adhesively secured thereto (see ElGURE 4). These ends 76 and 7b engage the edge portions S2 and 84 of the counterbalancing portion 50 of the blade when the blade is closed to prevent metal-to-metal impact of the blade and the frame. The portion of strip 72 which lies outwardly of edge 84? of flange 38 is slightly spaced from the edge portion 86 of blade portion Stl when the blade is closed. However, the felt is readily deformable under its own weight and also by air pressure to bend into scaling engagement with portion 86 of the blade to provide a dust seal therewith.

The improved weight means for providing closing force to the blade comprises an arm 88 -raving an inner portion 9% pivotally mounted on the web 52 of the blade by means of a bolt 92 as shown or by means of a rivet. The bolt or rivet secures arm 83 to the web 52 sufiiciently tightly to prevent movement of the arm from its adjusted position due to vibrations which occur in normal operation of the damper but allows manual rotation of the arm about its pivot from its outward pos- .on shown in FEGURE 1 to its inner or collapsed position shown by the dotted lines in FIGURE 1. It is seen that for packaging and shipping purposes, the collapsed position of arm 83 greatly reduces the exterior thickness dimension of the damper.

Arm $8 is bent to provide an outer portion 94 which as shown in FIGURE 5 extends a considerable distance to the right of its pivot 92. even when the blade is in a substantially horizontal position. The reason for so bending the arm is that if the frame is inaccurately positioned in the duct as shown by the dot-ted lines B in H6- URE 1, portion 94 of the arm will provide a closing force to the blade even though the blade is rotated in a clockwise direction beyond its horizontal position as shown by dotted lines B in FIGURE 1. When a sudden updraft causes the blade to rotate excessively in the counterclockwise direction to a position represented by A in FEGURE 1 or even to a further position to the left, the arm 8?, obviously still exerts a clockwise rotating force on the blade tending to restore it to either its wide open position or a lesser open position. This continuously applied clockwise rotating force therefore tends to prevent a sudden downdraft in the duct from catching the blade in the position A and keeping it open while the downdraft dust laden air r-ushes into the room. As aforesaid, stops could be provided on the frame or blade for preventing rotation of the blade to such a position that a downdraft might tend to maintain the blade open but such stops would prevent the blade from opening full wide when the frame, as shown in FIGURE 1, is inaccurately positioned as represented by dotted lines B therein. In this regard, it is noted that the inner shoulders 96 and 95 (see FIG- URES 1 and 6) formed by the termination of each of the side edges of blade portions 48 and 5! respectively of blade 16 are formed sufficiently far from the pivot 92 so as not to engage the top edge of flange 42 and the bottom of web 44 respectively when the blade 16 is swung to a full open position with the fraine '14 in its angular position represented by dotted lines B in FKGURE 1. It is noted, however, that should it be desired to provide a damper with stop means thereon for limiting the opening of the blade for certain applications, one or both of shoulders 96 and 98 located on blade portions 48 and 59 respectively may be located closer to the blade web 52 to provide convenient stop means for the blade.

A counterbalancing weight 1% is mounted on the blade portion 59 by such means as a bolt 102 and nut 104 and is swingably adjustable toward and away from the pivot axis 68 of the blade to either increase or decrease the effective closing moment produced by the arm 83. For example, if it is desired to decrease the effective closing force of arm 88, weight 1% with reference to FIGURE 1 may be adjustably rotated downwardly toward the flange 56 of blade portion 54 On the other hand, if it is desired to increase the closing force of arm 88, the weight 109 may be rotatably adjusted upwardly toward the pivotal axis 63 of the blade. The adjustment of the closing force of arm 88 by weight 1% may be termed as a crude one since the function of this weight is primarily that of equalizing the weight of the blade on either side of the pivotal axis 63 in order that a fine and sensitive adjustable closing force such as produced by 88 may be provided. It is readily seen that rotation of arm 88 to a position intermediate that shown in FIGURES 2 and 4 provides an infinite number of closing forces within a range of forces which are small relative to the large rotating forces which may be exerted on the blade by means of the weight 100. It is seen, therefore, that by the use of the two adjustments, weight 1% and arm 88, the pressure within an enclosure can be very sensitively maintained.

It is noted that applicants damper construction is such that by the use of heavier parts the damper may be employed in fireplace chimneys, stove and furnace flues, and the like. Moreover, regardless of the size or use of the damper, the operational as well as the manufacturing, packaging and shipping advantages of applicants improved construction are readily available.

While it will be apparent that the embodiment of the invention herein disclosed is well calculated to fulfill the objects of the invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. In a counterbalanced damper construction, a sheetlike damper comprising two substantially flat blade portions extending in generally opposite directions from a transverse intermediate pivot area, said blade portions lying in substantially parallel planes and being offset from one another, a step section substantially perpendicular to and joining said blade portions in said intermediate pivot area, fulcrum means in the pivot area for r-ockably supporting the damper, =a counterweight pivoted to said step section and swingable toward and from the damper about an axis which is substantially perpendicular to the fulcrum axis and parallel to the blade portions, one of said blade portions being shorter than the other, and additional counterweight means pivoted to the shorter blade and swingable along the plane of said shorter blade toward and from the fulcrum axis upon an axis which is perpendicular to said blade.

2. In a counterbalanced damper construction, a sheetlike damper comprising two substantially flat blade portions extending in generally opposite directions from a transverse intermediate pivot area, said blade portions lying in substantially parallel planes and being offset from one another, a step section substantially perpendicular to and joining said blade portions in said intermediate pivot area, fulcrum means in the pivot area for rockably supporting the damper, a counterweight pivoted to said step section and swingable toward and from the damper about an axis which is substantially perpendicular to the fulcrum axis and parallel to the blade portions.

References Cited in the file of this patent UNITED STATES PATENTS 1,623,286 Strahan Apr. 5, 1927 1,674,195 Droeger June 19, 1928 2,388,253 Dady Nov. 6, 1945 2,737,879 Cooke Mar. 13, 1956 

1. IN A COUNTERBALANCED DAMPER CONSTRUCTION, A SHEETLIKE DAMPER COMPRISING TWO SUBSTANTIALLY FLAT BLADE PORTIONS EXTENDING IN GENERALLY OPPOSITE DIRECTIONS FROM A TRANSVERSE INTERMEDIATE PIVOT AREA, SAID BLADE PORTIONS LYING IN SUBSTANTIALLY PARALLEL PLANES AND BEING OFFSET FROM ONE ANOTHER, A STEP SECTION SUBSTANTIALLY PERPENDICULAR TO AND JOINING SAID BLADE PORTIONS IN SAID INTERMEDIATE PIVOT AREA, FULCRUM MEANS IN THE PIVOT AREA FOR ROCKABLY SUPPORTING THE DAMPER, A COUNTERWEIGHT PIVOTED TO SAID STEP SECTION AND SWINGABLE TOWARD AND FROM THE DAMPER ABOUT AN AXIS WHICH IS SUBSTANTIALLY PERPENDICULAR TO THE FULCRUM AXIS AND PARALLEL TO THE BLADE PORTIONS, ONE OF SAID BLADE PORTIONS BEING SHORTER THAN THE OTHER, AND ADDITIONAL COUNTERWEIGHT MEANS PIVOTED TO THE SHORTER BLADE AND SWINGABLE ALONG THE PLANE OF SAID SHORTER BLADE TOWARD AND FROM THE FULCRUM AXIS UPON AN AXIS WHICH IS PERPENDICULAR TO SAID BLADE. 